Cellular Physiology

Cellular Physiology Indian Medical PG Question 1: Which electrolyte imbalance causes prolonged QT interval?

• A. Hypernatremia
• B. Hyperkalemia
• C. Hypocalcemia (Correct Answer)
• D. Hyponatremia

Cellular Physiology Explanation: ***Hypocalcemia*** - **Hypocalcemia** prolongs the **repolarization phase** of the action potential in cardiac myocytes, leading to a lengthened **QT interval** on an electrocardiogram. - This increased duration of repolarization places the heart at higher risk for **Torsades de Pointes** and other life-threatening arrhythmias [2], [3]. *Hypernatremia* - **Hypernatremia** primarily affects neurological function and can cause symptoms like **confusion** and **seizures**. - It does not typically lead to a **prolonged QT interval**; instead, it can sometimes be associated with a shortened QT interval or other non-specific ECG changes. *Hyperkalemia* - **Hyperkalemia** primarily causes peaked T waves, a widened QRS complex, and eventually **bradycardia** and **asystole** [1]. - While it drastically alters cardiac conduction, it typically **shortens** rather than prolongs the QT interval. *Hyponatremia* - **Hyponatremia** is associated with cerebral edema and neurological symptoms such as **headaches**, **nausea**, and **altered mental status**. - It generally does not cause a **prolonged QT interval**; significant hyponatremia can sometimes be associated with non-specific ECG changes [1] but not a specific lengthening of the QT interval.

Cellular Physiology Indian Medical PG Question 2: Reducing equivalents produced in glycolysis are transported from cytosol to mitochondria by ?

• A. Carnitine
• B. Creatine
• C. Malate-aspartate shuttle (Correct Answer)
• D. Glutamate shuttle

Cellular Physiology Explanation: ***Malate shuttle*** - The **malate-aspartate shuttle** is a primary mechanism for transporting **NADH reducing equivalents** from the cytosol to the mitochondrial matrix for **oxidative phosphorylation**. - It involves a series of **enzymes and transporters** that indirectly move electrons from NADH by converting **oxaloacetate to malate** in the cytosol, which then enters the mitochondria. *Carnitine* - **Carnitine** is primarily involved in the transport of **long-chain fatty acids** into the mitochondrial matrix for **beta-oxidation**. - It is not directly involved in the shuttle of NADH reducing equivalents generated during glycolysis. *Creatine* - **Creatine** and its phosphorylated form, **phosphocreatine**, are crucial for **energy buffering and transport** in tissues with high and fluctuating energy demands, like muscle and brain. - The creatine-phosphocreatine shuttle facilitates the rapid regeneration of ATP, but it is not involved in transporting glycolytic reducing equivalents. *Glutamate shuttle* - While glutamate and aspartate are components of the **malate-aspartate shuttle**, there isn't a standalone "glutamate shuttle" for transporting glycolytic reducing equivalents. - The **glutamate-aspartate transaminase** is an enzyme within the malate-aspartate shuttle, converting oxaloacetate to aspartate and alpha-ketoglutarate to glutamate from the matrix to the cytosol.

Cellular Physiology Indian Medical PG Question 3: Which one of the following conditions is caused by mutations in the gene that encodes the sodium-potassium-2-chloride cotransporter (NKCC2), and presents with sodium wasting, hypokalaemia, hypomagnesaemia and hypercalciuria?

• A. Bartter syndrome (Correct Answer)
• B. Fanconi syndrome
• C. Gitelman syndrome
• D. Alport syndrome

Cellular Physiology Explanation: ***Bartter syndrome*** - This syndrome is characterized by **loss-of-function mutations** in the **NKCC2 cotransporter** in the thick ascending limb of the loop of Henle, leading to impaired sodium and chloride reabsorption. - The resulting electrolyte imbalances include **sodium wasting**, **hypokalemia**, **hypomagnesemia**, and **hypercalciuria**. *Fanconi syndrome* - This syndrome involves a generalized defect in the **proximal renal tubules**, leading to impaired reabsorption of multiple substances including glucose, amino acids, phosphate, and bicarbonate. - It does not specifically involve a mutation in the NKCC2 cotransporter or present with the described electrolyte profile. *Gitelman syndrome* - This condition is caused by a mutation in the **thiazide-sensitive Na-Cl cotransporter (NCC)** in the distal convoluted tubule. - While it shares some features like hypokalemia and hypomagnesemia, it is typically associated with **hypocalciuria**, not hypercalciuria, and a different genetic defect. *Alport syndrome* - This is a genetic disorder affecting type IV collagen, primarily impacting the **glomerular basement membrane**, leading to hematuria, proteinuria, and progressive renal failure. - It is not associated with mutations in electrolyte transporters or the specific electrolyte abnormalities listed in the question.

Cellular Physiology Indian Medical PG Question 4: Which of the following is a late inward sodium channel blocker?

• A. Ranolazine (Correct Answer)
• B. Fasudil
• C. Ivabradine
• D. Trimetazidine

Cellular Physiology Explanation: ***Ranolazine*** - **Ranolazine** selectively inhibits the **late inward sodium current (I_Na)** in cardiac myocytes. - By reducing this current, it helps to decrease intracellular **sodium and calcium overload**, thereby improving myocardial relaxation and reducing angina and ischemia. *Ivabradine* - **Ivabradine** is a selective **funny channel (If) inhibitor** in the sinoatrial node. - It slows down the heart rate by reducing the rate of diastolic depolarization, primarily used for **chronic stable angina** and **heart failure**. *Fasudil* - **Fasudil** is a **rho-kinase inhibitor** used primarily in Japan and China for **cerebral vasospasm** following subarachnoid hemorrhage. - It works by inhibiting the phosphorylation of myosin light chain, leading to **vasodilation**. *Trimetazidine* - **Trimetazidine** is an **anti-ischemic metabolic agent** that inhibits the enzyme 3-ketoacyl-CoA thiolase, shifting cardiac metabolism from fatty acid oxidation to glucose oxidation. - This improves myocardial glucose utilization, which is more efficient in **ischemic conditions**, thereby reducing angina symptoms.

Cellular Physiology Indian Medical PG Question 5: What is the physiological condition in which the ratio of potassium permeability to sodium permeability (PK/PNa) is maximized?

• A. Depolarization
• B. Action Potential
• C. Resting Membrane Potential
• D. Hyperpolarization (Correct Answer)

Cellular Physiology Explanation: ***Hyperpolarization*** - During **hyperpolarization**, the membrane potential becomes more negative than the **resting membrane potential**, primarily due to the outflow of **potassium (K+)** ions or influx of **chloride (Cl-)** ions. - This increased K+ efflux or Cl- influx signifies a state where potassium permeability is maximal relative to sodium permeability, making the membrane less excitable. *Action Potential* - An **action potential** involves a rapid **depolarization** phase due to a massive influx of **sodium (Na+)** ions, causing the PNa/PK ratio to be high, followed by repolarization where K+ efflux restores the resting potential. - Therefore, during an action potential, the ratio of PK/PNa is at its lowest during the rising phase when sodium channels are open. *Depolarization* - **Depolarization** is characterized by a decrease in the absolute value of the membrane potential, making it less negative or even positive, primarily due to the influx of **sodium (Na+)** ions. - During depolarization, the permeability to sodium is significantly higher than to potassium, thus the PK/PNa ratio is low. *Resting Membrane Potential* - At **resting membrane potential**, potassium permeability is already much higher than sodium permeability due to **leak potassium channels**, but it is not maximized to the extent seen during hyperpolarization. - The resting potential is established by a balance of ion movements, primarily K+ efflux and limited Na+ influx, maintained by the **Na+/K+-ATPase pump**.

Cellular Physiology Indian Medical PG Question 6: In large neurons the nucleus can be found a large distance away from the terminal end of its axon. The body has a complex system of intracellular transporters that are able to carry essential proteins from the nucleus to the distal edge of the cell and back. Which of the following proteins are essential for this function?

• A. Kinesin, Troponin
• B. Myosin, Kinesin
• C. Actin, Dynein
• D. Dynein, Kinesin (Correct Answer)
• E. Glucose, Actin

Cellular Physiology Explanation: ***Dynein, Kinesin*** - **Kinesin** is primarily responsible for **anterograde transport** (from the cell body to the axon terminal) along microtubules, carrying vesicles and organelles. - **Dynein** handles **retrograde transport** (from the axon terminal back to the cell body), essential for recycling components and signaling. *Kinesin, Troponin* - While **Kinesin** is involved in axonal transport, **Troponin** is a protein found in muscle tissue that regulates muscle contraction, not intracellular transport in neurons. - Troponin binds **calcium ions** and influences the interaction between actin and myosin. *Myosin, Kinesin* - **Kinesin** is involved in microtubule-based transport, but **Myosin** is primarily associated with **actin filaments** for muscle contraction and intracellular movement, not long-distance axonal transport. - Myosin functions as a **motor protein** that converts chemical energy in ATP into mechanical force. *Actin, Dynein* - **Dynein** is crucial for retrograde axonal transport, but **Actin** is a structural protein forming microfilaments that are involved in cell shape, motility, and some short-distance transport, not the major long-distance axonal transport mechanism. - Actin filaments serve as tracks for **myosin motors**, primarily in the cell cortex. *Glucose, Actin* - **Glucose** is a sugar molecule, the primary energy source for cells, and not a transport protein. - **Actin** forms microfilaments for cell structure and short-range movement, not long-distance axonal transport as described.

Cellular Physiology Indian Medical PG Question 7: Insulin dependent glucose uptake occurs in:

• A. Brain
• B. Epithelial cells of small intestine
• C. Muscle (Correct Answer)
• D. Kidney

Cellular Physiology Explanation: ***Muscle*** - **Insulin** stimulates glucose uptake in **muscle cells** by promoting the translocation of **GLUT4 transporters** to the cell surface. - This process is crucial for removing glucose from the blood and storing it as **glycogen** in muscle tissue. - Along with **adipose tissue**, muscle is one of the **primary sites of insulin-dependent glucose uptake** in the body. *Brain* - The brain primarily uses **GLUT1** and **GLUT3 transporters** for glucose uptake, which are **insulin-independent**. - These transporters are always active, ensuring a continuous supply of glucose to the brain, regardless of insulin levels. *Epithelial cells of small intestine* - Glucose absorption in the small intestine initially occurs via **SGLT1** (sodium-glucose co-transporter 1) at the apical membrane and then exits into the bloodstream via **GLUT2** at the basolateral membrane. - This process is mainly regulated by the concentration gradient of glucose and sodium, not directly by **insulin**. *Kidney* - The kidneys reabsorb glucose from the filtrate primarily via **SGLT1** and **SGLT2** transporters in the renal tubules. - This reabsorption mechanism is **insulin-independent** and aims to conserve glucose, preventing its loss in urine.

Cellular Physiology Indian Medical PG Question 8: Absolute refractoriness of a neuron is due to?

• A. Hyperpolarization of Cl channels
• B. Opening of rectifier K+ channels
• C. Closure of activated Na channels
• D. Inactivation of Na channels (Correct Answer)

Cellular Physiology Explanation: ***Inactivation of Na channels*** - During the **absolute refractory period**, voltage-gated **Na+ channels** enter an inactivated state, making them unresponsive to further stimulation. - This inactivation prevents another action potential from being generated, regardless of the stimulus intensity, ensuring unidirectional propagation. *Hyperpolarization of Cl channels* - While **Cl- channels** can cause hyperpolarization, this typically leads to **inhibition** rather than absolute refractoriness. - Their activity doesn't directly prevent the generation of a new action potential by blocking Na+ channel function. *Opening of rectifier K+ channels* - The opening of **rectifier K+ channels** is involved in **repolarization** and the **relative refractory period**, by increasing K+ efflux. - While it contributes to making the neuron less excitable, it doesn't cause the absolute inability to fire associated with Na+ channel inactivation. *Closure of activated Na channels* - The **closure of activated Na+ channels** occurs as part of the repolarization process, but the critical mechanism for absolute refractoriness is their transition into an **inactivated state**, not simply closure. - **Inactivation** locks the channels in a non-responsive configuration, whereas simple closure would allow them to reopen quickly with sufficient depolarization.

Cellular Physiology Indian Medical PG Question 9: Which of these is true about the highlighted transporter?

• A. Both molecules go in
• B. One molecule goes in, other molecule goes out (Correct Answer)
• C. Both molecules go out
• D. One molecule goes in and two exit

Cellular Physiology Explanation: ***One molecule goes in, other molecule goes out*** - The highlighted transporter is the **Na+/K+ ATPase**, which actively pumps 3 **Na+ ions out** of the cell and 2 **K+ ions into** the cell, maintaining an electrochemical gradient. - This counter-transport (one molecule type going in and another going out) is characteristic of an **antiporter** pump. *Both molecules go in* - This option would describe a **symporter** mechanism where two different molecules move in the **same direction** across the membrane. - The Na+/K+ ATPase explicitly shows Na+ moving out and K+ moving in, which contradicts simultaneous inward movement. *Both molecules go out* - This would mean two molecules are expelled from the cell. The Na+/K+ ATPase, however, has K+ entering the cell. - While Na+ is pumped out by this transporter, K+ is actively transported inward. *One molecule goes in and two exit* - The Na+/K+ ATPase transports three Na+ ions out of the cell and two K+ ions into the cell, which is a 3:2 ratio and not one in and two out. - This option incorrectly describes the stoichiometry and directionality of ions for the Na+/K+ ATPase.

Cellular Physiology Indian Medical PG Question 10: With reference to human body's requirement for proteins, they are essential because they are: 1. an important alternative source for energy during specific metabolic states. 2. the primary molecules responsible for maintenance of osmotic pressure within the extracellular compartment. 3. critical for upkeep of cell mediated immune response. 4. vital for the synthesis of certain hormones. Which of the statements given above are correct?

• A. 2, 3 and 4
• B. 1, 2 and 3
• C. 1, 3 and 4 (Correct Answer)
• D. 1, 2 and 4

Cellular Physiology Explanation: ***1, 3 and 4*** - Proteins can be used as an **alternative energy source** during specific metabolic states, such as prolonged fasting or starvation, when carbohydrate and fat stores are depleted, through processes like **gluconeogenesis** and protein catabolism. - Proteins are critical for the **cell-mediated immune response**, as T-lymphocytes, cytokines, MHC proteins, and various immune mediators are protein-based. Protein-energy malnutrition significantly impairs cell-mediated immunity. - Many hormones, such as **insulin**, **growth hormone**, **ACTH**, and various **peptide hormones**, are protein-based or derived from amino acids, making proteins vital for hormone synthesis. *2, 3 and 4* - Statement 2 is **incorrect** because while proteins (particularly albumin) do contribute to osmotic pressure in the **intravascular compartment**, the statement refers to the "extracellular compartment" broadly, where **electrolytes (especially sodium)** are the primary molecules responsible for osmotic pressure maintenance, not proteins. - Proteins contribute to **oncotic pressure** (colloid osmotic pressure) specifically, which is distinct from total osmotic pressure. *1, 2 and 3* - This option incorrectly includes statement 2, which overstates the role of proteins in osmotic pressure across the entire extracellular compartment. - It correctly identifies proteins as an energy source and their role in cell-mediated immunity, but fails to include their vital role in **hormone synthesis**. *1, 2 and 4* - This option incorrectly includes statement 2 about osmotic pressure in the extracellular compartment. - It correctly recognizes proteins as an alternative energy source and for hormone synthesis, but omits their critical role in the **cell-mediated immune response**.

Cellular Physiology Flashcard 1 of 10

Question: _____ are glial cells that help mediate K+ ion metabolism

Answer: Astrocytes

Cellular Physiology Flashcard 2 of 10

Question: _____ distribution of protein channels increases diffusion capacity across a membrane

Answer: Increased

Cellular Physiology Flashcard 3 of 10

Question: Nernst potential is the _____cellular potential required to prevent the outward or inward movement of an ion

Answer: intra

Cellular Physiology Flashcard 4 of 10

Question: The _____ equation is used to calculate the diffusion potential when the membrane is permeable to several different ions.

Answer: Goldmann

Cellular Physiology Flashcard 5 of 10

Question: Axonemal _____ is an ATPase that links peripheral 9 doublets and causes bending of cilium (movement)

Answer: dynein

Cellular Physiology Flashcard 6 of 10

Question: The CFTR Cl- channel _____ (secretes or reabsorbs) Cl- in the sweat glands

Answer: reabsorbs

Cellular Physiology Flashcard 7 of 10

Question: _____ -soluble substances cross the membranes of capillary endothelial cells by simple diffusion

Answer: Lipid

Cellular Physiology Flashcard 8 of 10

Question: _____ on endothelial cells bind integrins on leukocytes, resulting in firm adhesion to the vessel wall

Answer: Cellular adhesion molecules (CAMs)

Cellular Physiology Flashcard 9 of 10

Question: _____ potential is calculated using the Goldmann Equation

Answer: Diffusion

Cellular Physiology Flashcard 10 of 10

Question: The distribution of _____ ions between intracellular and extracellular space is explained by the Gibbs-Donan equillibrium

Answer: diffusible